Cylinder boot



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CYLINDER BOOT Original Filed Nov. 19, 1962 INVENTORS Rana/0 Lfihell/museBY Carl A. Bier/em KW%I4M Their Affom y United States Patent 3,264,835YL1NDER BOUT Ronald L. Shellhause, Vandalia, and Carl A. litierlein,

Kettering, Ohio, assignors to General Motors Corporation, Detroit, Mich,a corporation of Delaware Original application Nov. 19, 1962, Ser. No.238,5ti3, now Patent No. 3,187,848, dated June 8, 1965. Divided and thisapplication Mar. 19, 1964, Ser. No. 353,035 Claims. (Cl. 74-182) This isa division of our copending application Serial No. 23 8,503, entitled,Wheel Cylinder Assembly and Method of Manufacture, and filed November19, 1962, now Patent No. 3,187,848.

The invention relates to a cylinder boot and more particularly to a bootof the type utilized in a wheel cylinder assembly for a wheel brake. Theinvention also relates to a boot which maybe received internally of theend of a wheel cylinder and is then held therein by friction andcohesive forces and mechanical locking engagement obtained by flowingthe wheel cylinder boot material into the engaged surface of the wheelcylinder. This is permitted by placing a retainer ring internally of theboot mounting flange with some of the boot material being radiallyoutward of the ring. In some instances it may be desirable to have thering at or adjacent the outer mounting surface. Such a constructioncould, for example, have a thin flashing of boot material on theradially outer portion of the ring. In some installations it may bedesirable to place the ring so that its radially outer surface is thesurface which engages the internal diameter of the wheel cylinder, withthe ring being press fitted into the wheel cylinder body. A wheelcylinder assembly having this construction is advantageous in that itvirtually eliminates damage to the wheel cylinder boot during varioushandling operations prior to being assembled in a wheel brake, andprovides for better radiant heat dissipation while the brakes areoperating. Assemblies embodying the invention also provide better wheelcylinder boot retention characteristics which increase within a fewhours after installation and further increase after a short period ofuseunder normal operating conditions. The boot retention and link pinsealing characteristics are such that the boot link pin sealing sectionflips outwardly should an abnormal gas or fluid buildup occur behind theboot and within the wheel cylinder. This flipping action functions as asafety valve which will allow only a small fiuid loss rather than acomplete fluid loss should the entire boot be forced away from the wheelcylinder. The sealing section will continue to have a sealing action inthe flipped condition. The internal position of the wheel cylinder bootalso permits better heat dissipation characteristics by exposing theentire outer surface of the wheel cylinder to radiant heat beingradiated from the brake shoes during the braking operation instead ofhaving the wheel cylinder boot covering the cylinder end and therebyacting as a radiant heat insulator in this area and at the same timeabsorbing more heat than it does when inside the cylinder.

In the drawing:

FIGURE 1 is a view of a portion of a wheel brake assembly embodying theinvention and having parts broken away and in section.

FIGURE 2 is a perspective view of a wheel cylinder and boot in positionjust prior to installation of the boot in the cylinder, with partsbroken away and in section.

FIGURE 3 is an enlarged partial view having parts broken away and insection and showing somewhat schematically the wheel cylinder boot asretained in the end of the wheel cylinder.

The wheel brake assembly may be of any suitable type and is illustratedin this instance as one of the duo-servo type. It includes a drum whichis rotatable and to 3,Zfi4,885 Patented August 9, i966 which the wheelis attached. A backing plate 12 is suitably attached to the vehicle. Ananchor pin 14 is secured to the backing plate to receive and transmitthe braking forces from the shoes 16 and 18 to the vehicle through thebacking plate. Shoes 16 and 18 are movably mounted on the backing platein the usual manner so that they are movable into and out of brakingengagement with the drum 1t). Suitable retractor springs 20 and 22 aresecured to the anchor pin 14 in the usual manner so that they performtheir usual functions, including retention of the guide plate 24 inplace on the anchor pin.

The wheel cylinder assembly 26 is secured to the backing plate 12 inforce-transmitting and heat conducting relationship in any suitablemanner. The particular wheel cylinder assembly illustrated includes acylinder body 28 in which a cylinder bore 30 is formed. Bore 30 issmooth finished by suitable operations such as honing, as is well knownto those skilled in the art. Only one-half of the interior of the wheelcylinder assembly 26 is illustrated in section since the other end ofthe assembly is substantially identical thereto but in reverse relation.The invention is also applicable to wheel cylinders of otherconstructions than those required for duo-servo brakes.

A piston 32 is operably received in the bore 3% and a cup seal 34engages the inner surface of the piston and is retained in positionagainst the piston by spring seat 36 and spring 38. Piston 32 issuitably recessed as at 40 to receive link pin 42 so that the link pinend 44 remains substantially on the center line of the wheel cylinder.Link pin 42 extends out of the wheel cylinder so that its other end 46engages the web 48 of shoe 18 in forcetransmitting relation. Thisportion of the structure is conventional except for the ends of thecylinder body 28, one of which is described below with regard to thewheel cylinder boot.

The wheel cylinder boot 50 is inserted in the end 52 of the cylinderbody 28 and is provided with an annular inner seal section 54 which isin sealing engagement with the link pin 42. Boot St) is preferablyconstructed somewhat like half of a hollow torus so that theintermediate body section 56 extends from the inner seal section 54first axially in one direction relative to the axis of the cylinder bodyand then curves as the radius increases until it extends axially in theother direction adjacent the outer peripheral section 58 of the boot.The outer peripheral section 53 is preferably radially outward of theinner seal section 54 and is formed as an annular cylindrical sectionhaving an outer surface 6%, an inner surface 62 and an end surface 64.The wheel cylinder boot is made of any suitable flexible material suchas rubber, neoprene, styrene butadiene, or any elastomeric materialhaving similar characteristics. Any material used must not be adverselyaffected by the hydraulic brake fluid utilized. It must also be able towithstand temperatures in the area of 300 F. to 450 F. without melting,cracking or otherwise failing. It must be sufficiently flexible topermit the inner seal section 54 to move with pivotal movement of linkpin 42 and to flip outwardly under excess pressure within the wheelcylinder body exteriorly of piston 32 without being permanently damaged.It must also be sufficiently strong to resist this flipping action untilsuch excess pressures are obtained. This, of course, is a function ofthe physical proportions of the boot, taking into consideration theother physical characteristics of the material utilized.

The boot 50 is preferably provided with a retainer ring 66 which can bebonded to the inner surface 62, or may otherwise be secured thereto. Forexample, ring 66 may be positioned radially intermediate the outersurface (at) and the inner surface 62 of the boot body. The outersurface of the ring would then be covered by a relatively thin flashingof boot material. The ring may also be positioned on the outer bootsurface 60, in an annular depressed section, so that the ring outersurface directly engages the wheel cylinder body with the boot materialadjacent the ring also engaging the wheel cylinder body to seal the bootin cooperation with the sealing action of the ring as the ring istightly fitted or pressed into the wheel cylinder body. When the ring ismounted on the boot inner surface 62, it is desirable to form the partof surface 62 in cylindrical engagement with the ring so that it is thebottom of a shallow recess which has approximately the thickness of theretainer ring 66 so that the retainer ring is positioned against a bootshoulder 68 and its edge 70 is substantially in alignment with the endsurface 64 of the boot. A similar construction may be utilized when thering is provided on the outer boot surface 60.

The recess 72 formed in the end 52 of the wheel cylinder preferably hasa greater diameter than the bore 30 so that a shoulder 74 is provided.The surface 76, which is the bottom of the recess 72, has a controlledfinish which is provided with a predetermined roughness. Where thefinish of bore 30 is honed to approximately a 15 microinches R.M.S.finish, surface 76 is finished so that it has a 60 to 120 microinchesR.M.S. finish. This range is given here as indicative of the roughnessbut is not so critical that the roughness must be maintained withinthese exact limits. It has been found, however, that these limits yieldsatisfactory results without requiring the close control in the finishoperation which is required in finish bore 30. The illustration inFIGURE 3 indicating the roughness of this surface is for illustrativepurpose only and is not indicative of the precise roughness desired.

The wheel cylinder boot 50 is installed in the recess 72 by pressing itaxially inward. A lubricant such as diacetone alcohol or a glycol ethersuch as commercially available brake fluid may be used. The lubricantmust assist in the installation without being so slippery that theimmediate friction and cohesive interaction of the wheel cylinder bodyand the boot is insufficient to resist the outward force exerted on theboot by spring 38 through cup 36 and piston 32. Also, the lubricant mustbe compatible with the material of which the boot is made. Since theboot outer cylindrical surface 60 is preferably provided with a diameterso that it is a slight interference fit in recess 72, the material ofwhich the boot is made is slightly compressed upon installation. Theboot is pressed axially into the recess 72, and by way of example, in aA3 wheel cylinder the installation force has been found to be from 10 to20 pounds. The boot is held in place by frictional engagement of itssurface 60 with the controlled finish surface 76 immediately uponinstallation, and this frictional engagement dependent to some extent onthe force exerted radially outward due to the interference fit. Theseforces are augmented by the relative stiffness of the retainer ring 66which resists radial collapse of the wheel boot and therefore exerts areaction force radially outward against the wheel cylinder body tendingto compress the boot section 58. It has been .found that immediateremoval of the boot 50 after such installation can be accomplished byexerting a removal (force axially against the retainer ring 66 which isapproximately half of the installation force. Thus at this time theremoval force is only required to overcome the frictional force plus aslight cohesive action. However, if the boot is permitted to set for atime without further work being done on or by the assembly, a removalforce approximately equal to the installation force is required. Thishas been found to be caused by the flow of the material of which theboot is made at and near surface 60 into the controlled roughnesssurface 76 so that these surfaces are mechanically locked. This isillustrated in FIGURE 3 in a non-scale presentation. This flow conditioncan be accelerated appreciably by exerting radial forces against theretainer ring 66 so as to cause the surface 60 Of the boot to flow morequickly into complementary engagement with the controlled finish surface76. This may also be accomplished by using the wheel cylinder at normalbrake operating temperatures for a short period of time. It has beenfound for example that after such usage the removal force required isapproximately double or triple the installation force. It is believedthat this occurs due in part to a cohesive reaction between the cylinderand the boot. It may also be due in part to some pressures being exertedinternally of the wheel cylinder boot in the chamber 78 formed by theboot, the piston 32, the link pin 42, and the cylinder body 28. Thesepressures are ogtained by normal movement of the piston 32 in the bore30 which alternately decreases and increases the volume of chamber 78.The heating of the wheel cylinder boot under operating conditions, aswell as the heating of the cylinder body, also contributes to the fullmechanical lock condition of the boot. Heat at or below the normaloperating temperature range of the boot, and therefore above ambienttemperatures can therefore be used to accelerate the mechanical lockcondition, or in conjunction with the radially outward forces notedabove, or independently of them. It is well known that elastomermaterials such as those of which boots may be made suffer a compressionset when compressed for long periods of time. This set in the section'58 of the boot does not decrease the removal forces required after somemonths, for example. It is thought that this set is counteracted by theeffectiveness of the cohesive and mechanical lock of the surfaces 60 and76. When ring 66 has its outer surface substantially flush with theextreme outer surface of the boot, that portion of the boot directlyengaging the wheel cylinder surface 76 will cooperate therewith toprovide the cohesive and mechanical lock.

It has been found that at times the shoe web temperatures will be ashigh as 850 F. for short periods when the brakes are temporarilyoverloaded. The heat is radiated from the drum and the shoes to thebacking plate, the wheel cylinder, the retractor springs, and any otherelements exposed to them in radiant heat relation. In previous commonlyused wheel cylinder constructions the wheel cylinder boots were madesufficiently large to be fitted tightly over the outside of the wheelcylinder ends. This construction is typical of all current productionbrakes of the duo-servo type. In this construction the ends of the wheelcylinder, which are the parts of the wheel cylinder bodies closest tothe shoe we'bs, are insulated by the boots. Thus the wheel cylindercannot function as a heat sink and heat transfer member wherein itreceives the radiant heat from the shoes and transmits it to the backingplate. Instead the outer peripheries of the wheel cylinder boots receiveextreme amounts of radiant heat under extreme brake conditions and tendto hold it without transferring it. By use of the structure embodyingthe invention however, the entire outer surface of the Wheel cylinderbody 28 is exposed to radiant heat from the shoe webs and, commonlybeing made of cast iron, readily absorbs this heat and transmits it tothe backing plate so that the boots are protected for an additionalperiod of time. This also tends to decrease the fade tendency of thebrakes since the heat is not retained as long as before. Also the wheelcylinder boot does not have its relative section exposed to theextremely high radiant temperature, but to a lesser temperature found inthe wheel cylinder body ends, therefore decreasing the likelihood offailure of the boot. In the particular mechanism embodying the inventionit is preferable to have all of the annular cylindrical outer peripheralsection 58 of the boot shielded by the end of the wheel cylinder. Thusdecreasing the radiant heat exposure of the boot to a minimum whilepermitting it to operate in the usual manner.

Another particularly important advantage of the invention is obtainedafter assembly of the wheel cylinder unit and during handling thereof.In prior construction units wherein the boot was put over the cylinderend, the boot would be almost invariably cut. If the wheel cylinder wasdropped from a height of approximately one foot to a solid surface suchas concrete floor, a work bench, or table, etc, this out may berelatively minute in many instances but forms a weak spot where highstresses occur and becomes the direct cause of premature boot failure.By placing the boot inside the wheel cylinder end as contemplated inaccordance with the invention, handling damage to the boot iseliminated, The wheel cylinder embodying the invention can be droppedfrom a height of five feet on most types of surfaces, including edges ofmachinery, benches, tables, etc., as well as concrete floors withoutdamage to the unit. In particular no cuts occur on the boot. This is anextremely important advantage in the manufacture of wheel cylinderassemblies since such assemblies are handled by hand or machinerynumerous times after being put together, not the least of which is thehandling of replacement wheel cylinders by mechanics in all types ofgarages.

In the claims:

1. A wheel cylinder boot for use with a brake wheel cylinder, said bootcomprising, an annular member having the inner periphery thereof forminga seal for sealing engagement with a wheel cylinder link pin and theouter periphery thereof being formed as a cylindrical section havingouter mounting and sealing and locking surface means for cohesive andmicromechanical locking engagement with an inner surface formed in oneend of a wheel cylinder, and a cylindrically formed retaining ring inengagement with the inner surface of the outer periphery cylindricalsection.

2. An elastorneric wheel cylinder boot having a cylindrical outerperiphery provided with outer mounting and sealing and locking surfacemeans for engaging a mating cylindrical inner surface of a Wheelcylinder in a boot retaining relationship and having a cylindricallyformed retainer ring received on the inner surface of said cylindricalouter periphery.

3. A wheel cylinder boot formed of an elastomeric brake fluid resistantmaterial to provide an annular link pin inner seal section and a centralannular body section extending from a direction axially parallel withsaid link pin seal section in one direction to an axially oppositedirection .as the radius thereof increases and having an annularcylindrical outer peripheral sealing and retaining section with theinner surface thereof having an annular cylindrically formed retainerring secured thereto and the outer periphery thereof being mounting andlocking surface imeans for engaging a Wheel cylinder controlledroughness surface for material flow to conform with the controlledroughness surface to provide a cohesive micromechanical lock therewith.

4. A wheel cylinder boot for use with a brake wheel cylinder, said bootcomprising, an annular member having the inner periphery thereof forminga seal for sealing engagement with a wheel cylinder link pin and theouter periphery thereof being formed as a cylindrical section havingouter surface means for cohesive and mechanical locking engagement withan inner surface formed in one end of a wheel cylinder, and acylindrically formed retaining ring in engagement with one surface ofthe outer periphery cylindrical section.

5. A wheel cylinder boot formed of an elastorneric brake fluid resistantmaterial to provide an annular link pin inner seal section and a centralannular body section extending from a direction axially parallel withsaid link pin se-al section in one direction to an axially oppositedirection as the radius thereof increases and having an annularcylindrical outer peripheral sealing and retaining section with oneperipheral surface thereof having a cylindrically formed annularretainer ring secured thereto and at least a portion of the outerperiphery thereof providing sealing and locking surface means adaptedfor engagement with a wheel cylinder controlled microroughness surfacefor material micro flow to conform with the controlled micro-roughnesssurface to provide a cohesive micromechanical lock therewith.

References Cited by the Examiner UNITED STATES PATENTS 2,120,922 6/1938Rasmussen 188152.82 X 2,249,141 7/1941 Johnson 277152 2,432,803 12/1947Rice 74-18.1 X 2,571,486 10/1951 Reynolds 188-152.82 X 2,729,109 1/ 1956Filliung 74-18.2 3,043,338 7/1962 Hanson 74--18.2 X

MILTON KAUFMAN, Primary Examiner. B-ROUGHTON G. DURHAM, Examiner.

1. A WHEEL CYLINDER BOOT FOR USE WITH A BRAKE WHEEL CYLINDER, SAID BOOTCOMPRISING, AN ANNULAR MEMBER HAVING THE INNER PERIPHERY THEREOF FORMINGA SEAL FOR SEALING ENGAGEMENT WITH A WHEEL CYLINDER LINK PIN AND THEOUTER PERIPHERY THEREOF BEING FORMED AS A CYLINDRICAL SECTION HAVINGOUTER MOUNTING AND SEALING AND LOCKING SURFACE MEANS FOR COHESIVE ANDMICROMECHANICAL LOCKING ENGAGEMENT WITH AN INNER SURFACE FORMED IN ONEEND OF A WHEEL CYLINDER, AND A CYLINDRICALLY FORMED RETAINING RING INENGAGEMENT WITH THE INNER SURFACE OF THE OUTER PERIPHERY CYLINDRICALSECTION.